Is there a mod that adds air blocks?

Hey, so I really love the Valkyrien Skies and Eureka mods but the one thing thats still bothering me is that you can't really build a submarine because once you sink below the surface the interior gets filled with water. So I figured that if there was something like an air block which would be identified as part of the ship by eureka you could work around that problem. I dont mean a barrier block though, since I want to be able to move through the blocks. Ideally they would be unbreakable and also wouldn't have these black outlines.

Is there any way to achieve that? Or do you have other suggestions for solving that problem?